Constant-pressure pinch rolls for continuous casting



Aug. 2, 1966 H. s. ORR ETAL 3,263,284

CONSTANT-PRESSURE PINOH ROLLS FOR CONTINUOUS CASTING Filed D60. 20, 1963 4 Sheets-Sheet 1 INVENTORS HOWARD s. ORR

BY JOHN H:RICHARDS ATTORNEY S Aug. 2, 1966 H. s. ORR ETAL PRESSURE PINOH ROLLS FOR CONTINUOUS CASTING Filed Dec. 20, 1963 4 Sheets-Sheet 2 INVENTORS HOWARD S. ORR JOHN H. RICHARDS ATTORNEY S Aug. 2, 1966 H. s. ORR ETAL.

CONSTANT-PRESSURE PINCH ROLLS FOR CONTINUOUS CASTING 4 Sheets-Sheet 5 Filed Dec.

INVENTORS S- ORR H R I CH ARDS HOWARD ATTORNEYS Aug. 2, 1966 H. s. ORR ETAL 3,263,284

CONSTANT-PRESSURE FINCH ROLLS FOR CONTINUOUS CASTING 4 Sheets-Sheet 4 Filed Dec. 20, 1963 INVENTORS HOWARD S. ORR BY JOHN HuRICHARDS w fl,

ATTORNEYS United States Patent 3,263,284 CONSTANT-PRESSURE llNCH ROLLS FOR CONTINUOUS CASTING Howard S. Orr, Upper t. Clair Township, Allegheny County, and John H. Richards, Penn Hills Township, Allegheny County, Pa., assignors to United States Steel Corporation, a corporation of Delaware Filed Dec. 20, 1963, Ser. No. 332,056 6 Claims. (Cl. 22--57.2)

This invention relates to continuous casting apparatus which includes pinch rolls for controlling the rate of descent of a casting, and more particularly to apparatus for maintaining a uniform lateral pressure exerted by the pinch rolls against the casting.

Conventional apparatus for continuous casting of metals such as iron and steel includes a mold having a passage therethrough which is open at the upper end for the introduction of molten metal and open at the lower end for discharge of a partially solidified casting, a cooling section below the mold which includes a plurality of water sprays for cooling the surfaces of the casting and a plurality of guide rolls for supporting the side walls of the casting and for guiding it in a vertical path, and one or more sets of pinch rolls below the cooling section for controlling the rate of descent of a casting.

The mold is water cooled and has a cross-sectional hape approximately the same as that desired in the castmg.

The lower end of the mold passage is closed during the pouring of metal by means of a suitable plug such as a starter bar. This starter bar is inserted upwardly through the pinch rolls and the cooling section into the lower end of the mold prior to the start of casting. Molten metal is then poured into the mold. A skin of metal adjacent the mold walls solidifies against the upper end of the starter bar and the mold walls while the starter bar is still in the mold. When the metal reaches a predetermined level in the mold, the starter bar with the partially solidified casting attached thereto is lowered under the control of the pinch rolls.

The amount of lateral pressure exerted by the pinch rolls against the casting depends on the relationship between the spacing between the rolls and the thickness of the casting. If the casting is thinner than the spacing between the pinch rolls, the rolls obviously exert no pressure at all against the casting. If the casting is thicker than the spacing between the pinch rolls, the rolls exert lateral pressure against the casting which is approximately proportional to the difference between the thickness of the casting and the pinch roll spacing. Since metals such as steel are very nearly incompressible, even at the elevated temperatures at which the metal passes through the pinch rolls, minor differences in thickness of the casting result in major differences in pinch roll pressure.

Minor diiierences in the thickness of a casting generally occur at different points along the length thereof. This results in variations in pinch roll pressure, which may range from zero to amounts substantially in excess of the pressure necessary to maintain control of the rate of descent and even great enough to harm the crystalline structure of the casting. Frequently the casting still has a small core of unsolidified metal in its center as it descends through the pinch rolls. Such castings are particularly apt to be damaged by excessive pinch roll pressure.

The principal object of this invention is to provide an apparatus for automatically varying the distance between pinch rolls in response to variations in the thickness of the casting, so that the pinch rolls will maintain a uniform pressure against the casting at all times.

This invention will now be described in detail with reference to the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of the apparatus of this invention;

FIG. 2 is a side elevation of the apparatus of this invention;

H6. 3 is a top plan view of the apparatus of this invention;

FIG. 4 is a view along line 44 of FIG. 3, showing a side elevation of a portion of the apparatus with parts in section;

FIG. 5 is a diagrammatic illustration of the control mechanism for controlling the apparatus of this invention.

Referring now to the drawings, 10 indicates generally a supporting structural framework which includes a platform or floor 12 on which the apparatus of this invention is mounted. The apparatus is mounted on a frame 14, which is supported above the floor 12 by blocks 16. This frame includes two pairs of structural members as for example I-beams 18, one above the other, transverse horizontal beams (not shown) joining the beams in each pair, and vertical supports or columns 26 joining the upper and lower I-beams 18. The structure of frame 14 may differ from that shown, as long as four horizontal surfaces suitable for mounting bearing blocks for the pinch rolls are provided. Guideways 22 and 24 are fixedly mounted on each of the I-beams 18, on either side of the path of the casting. Guideway 22 has a bearing block 26 fixedly mounted therein. A horizontally reciprocable bearing block 28 is mounted in guideway 24 for horizontal movement toward and away from bearing block 26.

A pair of pinch rolls 3% and 31 are journaled in hearing blocks 26 and 28 respectively, positioned to receive therebetween a continuous casting 32. Roll 36 has a fixed axis, and will be referred to herein as a fixed pinch roll. The rolls are conventional motor driven rolls of large diameter, and are journaled in a conventional maner in bearing blocks 26 and 28. However, pinch roll structures other than the illustrated structure may be substituted. For example, a set of pinch rolls comprising several rolls of small diameter bearing against each of the two opposed faces of the casting, with means for driving all rolls at the same speed, may be provided in place of the pair of rolls 30 and 31.

One or more strain gauges 33 are provided for measuring the lateral pressure exerted by the casting against the pinch roll 30 and the stationary bearing block 26 in which it is mounted. These are conveniently mounted on columns 20. Force exerted by the casting on pinch roll 30 is transmitted through stationary bearing block 26, producing a small movement which varies as the force and which is registered by the strain gauges. Any known strain gauge may be used.

A pair of spring retaining plates 34 and 36 are mounted for reciprocating movement in guideway 24. Plate 34 normally abuts against bearing block 28. One or more tie bolts 38 connect the spring retaining plates 34 and 36, so as to prevent the distance between these two plates from exceeding a predetermined maximum. A plurality of heavy compression springs 40 are provided in the space between spring retaining plates 34 and 36. These compression springs urge bearing block 28 and roll 32 journaled therein toward the fixed bearing block 26 and the pinch roll 30 journaled therein.

A manually movable back-up plate 4.2 of substantial thickness is mounted for reciprocation in guideway 24. This back-up plate is movable independently of spring retaining plate 36, but abuts against spring retaining plate 36 while a casting descends through the pinch rolls. A pair of externally threaded screws 44 of substantial length are secured to back-up plate 42. Housings 45 surround the midportions of screws 44 and house worm gears through which screws 44 are turned. A hand wheel 46 mounted on shaft 48 is provided for turning screws 44 and thereby moving back-up plate 42 toward or away from fixed bearing block 26. The position of back-up plate 42 is pre-set according to the thickness of the desired casting before the casting is commenced.

Means are provided for opposing the force of springs 40 so as to maintain a constant roll pressure. These means include two pairs of single acting hydraulic cylinders 52, which are secured to frame 14, and which have piston rods 54 extending through both ends thereof. Piston rods 54 are operatively connected at one end to bifurcated mounting attachments 56 and pivot ears 58, which are attached to the reciprocable bearing block 28. Bolts 68 secure attachment members 56 to pivot ears 58. Cylinders 52 are provided with inlets 62 for the admission of a fluid under pressure.

It is desirable to maintain the axis of roll 31 parallel to the axis of roll 30 at all times. To this end an equalizing mechanism (best illustrated in FIG. 3) indicated generally at 64 is provided. This equalizing mechanism includes a cross bar 66 operatively connected to the ends of piston rods 54 which are remote from bearing block 28 by means of a bifurcated connector 68 attached to each of the piston rods 54 and bolts 70 securing cross bars 66 to connector 68. The mechanism 64 also includes a toggle arrangement 72 which comprises two pairs of links 74 secured together by cross bar 76 and bolted to cross bar 66 and to a second cross bar 78, which is fixedly secured to frame 14. Bifurcated mounting ears 80 secure links 74 to cross bars 66 and 78.

Referring now to FIG. 5, an electric signal from strain gauges 33 is transmitted to a differential signal generator 82. The differential signal generator is pre-set to a desired pinch roll pressure. This generator then generates an electric current directly proportional to the difference between this pre-set pinch roll pressure and the actual pinch roll pressure as determined by strain gauges 33. The direction of current is determined by whether the actual roll pressure or the pre-set roll pressure is greater. Any known type of differential signal generator which operates in this manner can be used.

A hydraulic pumping unit 84 including a fluid reservoir 86, a pipeline 88 for delivering fluid from said reservoir to a reducing valve 90, and a return line 92 for returning said fluid to the reservoir 86 is provided. Static pressure lines 94 communicate between the low pressure side of valve 90 and each of the cylinders 52 through opening 62. The differential signal generated by generator 82 is transmitted through line 96 to valve actuator 98, which controls the position of valve 90.

When strain gauges 33 register an excess of pinch roll pressure over the pre-selected level, the differential signal transmitted through line 96 causes valve actuator 98 to open valve 90 to a wider opening, and thereby establish a higher outlet pressure. This higher outlet pressure is transmitted through hydraulic line 94 to the cylinders 52, increasing the pressure therein and moving the pistons located in said cylinders to the right, and thereby moving bearing block 28 away from fixed bearing block 26. If the pinch roll pressure falls below the pre-selected level, the differential signal transmitted through line 96 will move valve actuator 98 in the opposite direction, throttling down valve 90 and reducing the outlet pressure in said valve, thereby lessening pressure in hydraulic line 94 and cylinders 52 and casting bearing block 28 to be moved toward bearing block 26 by the force of compression springs 40.

In operation, the position of reciprocable bearing block 28 and pinch roll 31 is pre-set manually by handwheel 46 so that the spacing between rolls 30 and 31 is the same as the thickness of the casting. When the pinch roll 31 has been previously positioned for a thicker casting than that desired, the handwheel 46 is turned so as to move back-up plate 42 toward fixed pinch roll 30. This in turn causes spring retaining plates 34 and 36, movable bearing block 28 and pinch roll 31 to move toward fixed pinch roll 30. When the pinch roll 31 has been previously positioned for a thinner casting, handwheel 46 is turned so as to' move back-up plate 42 away from fixed pinch roll 30. This causes the back-up plate 42 to be moved out of contact with spring retaining plate 36. Pumping unit 84 is then turned on, establishing fluid pressure in static pressure lines 96 and cylinders 52. This moves bearing block 28 and pinch roll 31 away from fixed pinch roll 30 until spring retainer plate 36 is once more in contact with back-up plate 42. Springs 40 provide no opposition to hydraulic cylinders 52 while spring retaining plate 36 is out of contact with back-up plate 42. Once contact between spring retaining plate 36 and back-up plate 42 is re-established, further movement of pinch roll 31 away from pinch roll 30 is against the bias of springs 40.

After the position of pinch roll 31 has been set, a starter bar is inserted upwardly through pinch rolls 30 and 31 and the guide rolls thereabove into the discharge opening of a mold. Molten metal is poured into the mold to form a continuous casting 32. When a skin of metal has solidified around the side walls of the mold and at the end which is adjacent to the starter bar, the starter bar with the casting attached is lowered under the control of pinch rolls 3t) and 31, which are driven at a predetermined constant speed. Pinch rolls 30 and 31 contact the starter bar during the initial period of descent. After the starter bar descends below the elevation at which the pinch rolls are located, the pinch rolls contact the two parallel faces of the casting.

Minor variations in the thickness of a casting may occur during the course of a casting. These variations cause variations in the pressure exerted by the casting on pinch rolls 30 and 31. These variations are registered by strain gauges 33, which cause bearing block 28 and movable pinch roll 31 to be moved toward or away from the fixed bearing block 26 and pinch roll 30 in the manner indicated previously, to maintain a substantially constant pinch roll pressure at all times.

Various modifications can be made by those skilled in the art without departing from the spirit of this invention. Accordingly the scope of this invention shall be limited only by the scope of the appended claims.

What is claimed is:

1. Apparatus for maintaining a constant pinch roll pressure in a continuous casting system comprising a pair of fixed bearing blocks, a pair of reciprocable bearing blocks which are movable toward and away from said fixed bearing blocks, at least one pinch roll journaled for rotation in said pair of fixed bearing blocks, at least one pinch roll journaled for rotation in said pair of reciprocable bearing blocks, said pinch rolls adapted to confine a casting passing therebetween and in contact therewith, means for continuously measuring the force transmitted to the fixed bearing blocks from the casting, means for transmitting a signal which is proportional to the difference between said measured force and a preselected force, and means for moving said reciprocable bearing blocks toward and away from said fixed bearing blocks in response to said differential signal.

2. Apparatus for maintaining a constant pinch roll pressure in a continuous casting system comprising a pair of fixed bearing blocks, a pair of reciprocable bearing blocks which are movable toward and away from said fixed bearing blocks, at least one pinch roll, journaled for rotation in said pair of fixed bearing blocks, at least one pinch roll journaled for rotation in said pair of reciprocable bearing blocks, said pinch rolls adapted to confine a casting passing therebetween and in contact therewith, spring means urging said reciprocable bearing blocks toward said fixed bearing blocks, fluid pressure operated means opposing the force of said spring means, means for continuously measuring the force transmitted to the fixed bearing blocks from the casting, means for transmitting a signal which is proportional to the difference between said measured force and a preselected force, and means for moving said reciprocable bearing blocks in response to said differential signal.

3. Apparatus according to claim 2 in which said fluid pressure operated means includes at least one fluid pressure operated cylinder, said apparatus also including manually operated means for moving said reciprocable bearing blocks.

4. Apparatus for maintaining a constant pinch roll pressure in a continuous casting system comprising a pair of pinch rolls adapted to contact opposite faces of a continuously formed casting as it descends and thereby control the speed of descent of the casting, a pair of fixed bearing blocks in which one of said pinch rolls is journaled for rotation, a pair of reciprocable bearing blocks in which the other of said pinch rolls is journaled for rotation, said reciprocable bearing blocks being movable toward and away from said fixed bearing blocks, spring means urging said reciprocable bearing blocks toward said fixed bearing blocks, fluid pressure operated means opposing the force of said spring means for moving said reciprocable bearing blocks away from said fixed bearing blocks, means for continuously measuring the force transmitted to the fixed bearing blocks from the casting, means for transmitting a signal which is proportional to the difierence between said measured force and a preselected force, and means responsive to said signal for controlling the admission of fluid under pressure to said fluid pressure means and thereby moving said reciprocable bearing blocks so as to maintain a predetermined constant pinch roll pressure.

5. Apparatus according to claim 4 in which said fluid pressure means includes at least one fluid pressure operated cylinder.

6. Apparatus according to claim 4 including manually operated means for moving said reciprocable bearing blocks.

References Cited by the Examiner UNITED STATES PATENTS 2,691,326 10/ 1954 McArn. 3,090,534 5/1963 Frommer et a1. 226l80 X 3,112,537 12/1963 Hess et a1 22-57.2

J. SPENCER OVERHOLSER, Primary Examiner. 

2. APPARATUS FOR MAINTAINING A CONSTANT PINCH ROLL PRESSURE IN A CONTINUOUS CASTING SYSTEM COMPRISING A PAIR OF FLEXED BEARING BLOCKS, A PAIR OR RECIPROCABLE BEARING BLOCKS WHICH ARE MOVABLE TOWARD AND AWAY FROM SAID FIXED BEARING BLOCKS, AT LEAST ONE PINCH ROLL, JOURNALED FOR ROTATION IN SAID PAIR OF FIXED BEARING BLOCKS, AT LEAST ONE PINCH ROLL JOURNALED FOR ROTATION IN SAID PAIR OF RECIPROCABLE BEARING BLOCKS, SAID PINCH ROLLS ADAPTED TO CONFINE A CASTING PASSING THEREBETWEEN AND IN CONTACT THEREWITH, SPRING MEANS URGING SAID RECIPROCABLE BEARING BLOCKS TOWARD SAID FIXED BEARING BLOCKS, FLUID PRESSURE OPERATED MEANS OPPOSING THE FORCE OF SAID SPRING MEANS, MEANS FOR CONTINUOUSLY MEASURING THE FORCE TRANSMITTED TO THE FIXED BEARING BLOCKS FROM THE CASTING, MEANS FOR TRANSMITTING A SIGNAL WHICH IS PROPORTIONAL TO THE DIFFERENCE BETWEEN SAID MEASURED FORCE AND A PRESELECTED FORCE, AND MEANS FOR MOVING SAID RECIPROCABLE BEARING BLOCKS IN RESPONSE TO SAID DIFFERENTIAL SIGNAL. 